Thermionic valve circuits



Patented Aug. 2, 1927.

A' onlin-:DYy STATES PATENT OFFICE.

. THERMIONIC 'VALVE CIRCUITS.

Application led October 27, 1926, Serial No. 144,554, and in Great Britain July 2, 1925'.

This invention relates to thermionic valve circuits in which means are embodied for neutralizing the capacit coupling between the elements of an amp ifler.

It is well known in an amplifier in which inductances are respectively connected in the plate and grid circuits of a thermioni'c valve to neutralize the capacitative coupling be-v tween the two circuits by coupling an auxiliary inductan'ce closely to either of the said inductances and connecting said auxiliary inductance through a condenser to the other of said inductances. y.

This arrangement however has the disadvant-age that the capacity of the said condenser is added to the capacity in either the plate or the grid circuit and therefore unless said condenser is made very small the said circuit will become loaded with excessive capacity.

In accordance with the present invention I employ coupled respectively to said inductances-preferably as closely as possible-two auxiliary inductances connected together through a condenser orcondensers so as to form a closed circuit. These auxiliary inductances are preferably of fewer turns than said inductances'to which they are coupled. The capacity connecting them may then be made large in comparison with the capacity it is desired to neutralize. This is of course advantageous from the point of view of production.

Each of Figs.v 1 and/2 of the accompanying drawings illustrates diagrammatically theapplication of the invention to a single stage ampliier'.A Fig. 3 illustrates the application of said invention to a multi-stage amplier comprising an interstage inductance which is connected in the plate circuit of one valve and the grid' circuit of the next.

Referring first to Figures 1 and 2 each-illustrates a valve fu, one oscillatory circuit (consisting of an inductance 'il in parallel with a condenser 01) connected in the grid circuit of the valve, and another oscillatory circuit (consisting of an inductance i in parallel with a condenser o2) connected in the plate circuit and the valve.

These two figures also each illustrate ltwo auxiliaryv inductances a1 and az respectively coupled with the inductance's il and i2 and connected together through a capacity so as to form a closed circuit. In Fig. 1 it consistsof a single condenser c3. In Fig. 2 it consists of two condensers c4 and c5 connected 'in circuit alternately with the auxiliaryl inductances.

The'values of the several capacities and inductancesare selected for neutralization of thev capacitative coupling between the elements. That is to say, for close coupling, if

1 d .bersagli 2 turns 1n a turns in a and if the valve capacityc v and the total capacit in circuit a1, a2=Cn then for neutralization Cn =n1 n2 v Cc Therefore if Cn r Referring to Fig. 3, the multi-stage ampliier therein illustrated comprises two valves o1 and v2. The valve v1 has an oscillatory circuit (consisting of an inductance l in parallel with a condenser c1) connected in the grid circuit thereof and the valve o2 has an oscillatory circuit (consisting of an inductance .i2 in parallel with a'condenser 02) connected inthe platecircuit thereof. Between the two 'valves is a third oscillatory circuit (consisting of an inductance 12 in parallel with a condenser cl2), said circuit being connected in the plate circuit of the valve /vl and the grid circuit of the valve o2. This third oscillatory circuit is of course not connected directly to the filament circuit of the valves and, in accordance with the usualpractice a high resistance fr is connected between the grid and filament of the valve o2 and a capacity p between the grid of said valve and said'third oscillatory circuit.

In this case there are three auxiliary inductances a1, a2 and as coupled respectively to the inductances 1f/12 and The inductances a1 and a2 are connected in a closed circuit with a condenser c and the inductances a2 and a3 are connected in a closed cir- Y cuit with a condenser o7. This arrangement might obviously however be similar to that might be connected in each of the closed circuits alternately with the auxiliary inductances.

I the circuit comprising l scribed embodiments The values of the capacities and inductances are calculable inthe same way'. as in the case of Figs. 1 and 2, the two valves being considered separately.

Obviously multi-stage amplifiers comprising any number of valves greater'than two may be arranged in amanner analogous to the arrangement illustrated in Fig. 2.

Preferably. in each of the three above dethe auxiliary inductances are conductively connected. to an earthy point of the amplifier, one point of them being connected to the filament circuit.

It will be clear that the present invention may be used inl'oue amplifier in combination with the invention claimed in my copending application Serial No. 144,553 of even date herewith so that both the capacitative and the magnetic coupling between the elements of the amplifier may be neutralized.

For example this combination will be effected by connecting an inductance in shunt with the condense-Nc of Figure .1, or by connecting respective impedances in shunt with the capacities c and c7 of Figure.

It has been found in some cases that although electrostatic coupling has been neutralized between adjacent stage the instrument is still notI stable owing to coupling between remote stages. In such cases. an auxiliary neutralizing circuit such as described above for neutralizing` the coupling between adjacent stages may be used for neutralizing any such capacity coupling between 'stages not adjacent which may have` capacity coupling between them.

What I claim and desire. to Secure by Letters Patent is l. In a tlierinioiiic valve amplifier coin-A prising inductances respectively connected in plate and grid circuits and in whic'h capacitative coupling exists between certain of the amplifier elements. means for neutralizing said capacitative coupling. said means comprising auxiliary inductances and a condenser 4connected in a closed circuit said auxiliary inductances being electrocoupled respectively to said plate, and grid circuit inductances. 2'.l In a magnetically,

in'plate and Vgrid circuits andin which ca-y izing said capacitative coupling, said means comprising auxiliary inductances and a condenser connected in a closed circuit a' promt of which is connected to an"earth point, said auxiliaryinductances being electromagnetically coupled respectively to said plate and grid circuit inductances.

3. In a multi-'stage amplifier comprising two valves, an inductancc connected to the grid of -the first valve. an inductanceconnected `to the plate of' the second valve and an inductance connected both to the plate of the first valve and the grid of the second valve, -and in which capacitative coupling exists between certain of the elements of the means for neutralizing 'said caamplifier, pacitative coupling said means comprising three auxiliary inductances each connected in a closed circuit with the next and condensers connected respectively in said closed circuits. said auxiliary inductances' being respectively coupled to said former inductances. l

4:'. In a multi-stage amplifier comprising two "valves, an. inductance connected to the grid of the first valve, an inductance' connected to the plate of' the second valve and an inductance connected both-to the plate of 'the first valve and the grid of the second valve` and in lwhich capacitative coupling exists between certain of theelements of the amplifier, means for neutralizing` said capacitative coupling, said means comprising three auxiliary inductances eac-hv connected in a closed circuit with the next and coni densers connected respectively in said closed circuits, said auxiliary inductances being respectively coupled to said former inductances and said closed circuits heilig each connected to an. earthy point.'

In witness whereof I affix my signature.

PETER WILLIAM IVILLANS.

tlierinionic valve amplifier comprising inductances respectively connected` Veo 

